Recently, videoconference systems have been widely adopted. These videoconference systems are for videoconferencing between remote locations through a communication network such as the Internet.
Such a videoconference system enables a conference to be conducted between remote locations in an environment which is close to an actual conference environment. During videoconferencing, one of parties (participants) participating in the videoconference is located in one of conference rooms, and the other party is located in the other conference room. A transmission terminal device (a terminal device) of the videoconference system located in the one of the conference rooms photographs images of the conference room and the participants, and the transmission terminal device collects audio data. The transmission terminal device converts the collected data into digital data and transmits the digital data to the other party's transmission terminal device. The other party's transmission terminal device causes a display (display device) disposed in the other conference room to display the images, and outputs sound through a speaker.
Such a transmission terminal device of the videoconference system has been sold with a display as a videoconference set. However, cases have been increasing where only a single transmission terminal device is sold. Therefore, recently, there are many transmission terminal devices that can be connected to various types of displays having different types of resolution.
Further, cases have been increasing where a transmission terminal device can be connected to a display through an interface conforming to a High-Definition Multimedia Interface (HDMI), which is for an audio-visual (AV) appliance such as a digital television, besides a conventional RGB interface (an interface for the Red-Green-Blue color model) and a digital visual interface-digital (DVI-D). A display of a digital television conforming to the HDMI standard is capable of displaying at a high resolution such as a resolution of 1280 pixels (width) by 720 pixels (height) (hereinafter, denoted as 1280×720).
Even if a transmission terminal device does not include an interface conforming to the HDMI standard, an image can be displayed at a high resolution by connecting the transmission terminal device to a display by using a conversion cable that converts a HDMI signal into a DVI-D signal, provided that the transmission terminal device includes an interface conforming to the DVI-D standard.
Whereas, the Video Electronics Standards Association (VESA) discloses the Extended Display Identification (EDID) as a data structure standard for transmitting capability information indicating a capability of a display to a transmission terminal device. Based on this standard, a display usually stores unique EDID information in a memory included in the display. The EDID information includes data such as information regarding displaying timing of the display and information regarding resolution of the display. The transmission terminal device sets the resolution of the connected display by using a value based on the EDID information.
In the latest version of the EDID, in addition to defining data in conventional basic data fields, extended data fields have been developed so that the standard is compatible with a new standard such as the HDMI.
However, when the conversion cable is utilized, only the basic data fields are transmitted to the transmission terminal device. The extended fields are not transmitted. Therefore, the transmission terminal device is not able to control all the range of the resolution within which the display can display an image.
However, since recommended resolution of the display has been described in the basic data fields of the EDID, it is possible to utilize the recommended resolution.
In general, the recommended resolution defines the maximum (native) resolution at which the display is capable of displaying an image.
Since the transmission terminal device can only refer to the basic fields of the EDID, the transmission terminal device is not able to select the resolution defined in fields other than the basic fields. For example, when the transmission terminal device is connected to a display that is capable of displaying at a resolution of 1920×1080, and when it is described in the extended fields that the display is capable of displaying at a resolution of 1280×720, the transmission terminal is not able to select the resolution of 1280×720 nor change the resolution into the resolution of 1280×720.
When a sufficient memory is ensured in the transmission terminal device, the transmission terminal device may display an image at the resolution of 1920×1080 by selecting the recommended resolution. However, when the transmission terminal device is not capable of displaying an image at the resolution of 1920×1080, which requires a large display memory, due to a cost problem, the transmission terminal device has no choice but to display the image at default resolution of 1024×768, which is lower than the resolution of 1280×720.
Whereas, Patent Document 1 (Japanese Patent Laid-Open Application No. 2010-256794) discloses an electronic device that is capable of setting desired customized resolution depending individually on a displaying device, without introducing special hardware. Specifically, the electronic device includes a retrieval means for retrieving EDID information stored in a display; a determination means for determining a piece of customized EDID information corresponding to the retrieved EDID information retrieved by the retrieval means among plural pieces of customized EDID information corresponding to various types of displays, wherein the plural pieces of customized EDID information have been stored; and a providing means for providing the determined customized EDID information that has been determined by the determination means to a display control means for controlling an indication on the display based on the EDID information.
However, since the above-described electronic device can only refer to the basic data fields of the EDID, the device is not able to display an image at resolution other than the resolution defined in the basic data fields. Namely, the above-described problem is not resolved by the electronic device.
Hereinabove, the case has been explained for the transmission terminal device. However, the explanation is also applied, in general, to an electronic device that outputs image data to an external display.